I’d like to blame the tool, but…

Agree with @jwmelvin looks like you were off the timing mark a few times. If you can slow it down, practice just getting engagement on the mark every time. What matters is consistency. Later you can speed it up as your consistency improves. It's developing eye hand coordination as well as muscle memory.

Some of the crests have additional cuts in them which shows inconsistent timing of lead screw engagement. You can see them if you zoom way in to your picture. When you get it right the threads will appear a lot cleaner. You are almost there!
 
Thanks guys, I hadn't noticed the double cuts. I was trying to hit the half nut at the "1" everytime, I don't think I missed it by more than 1/4 of an increment, but I'll pay closer attention.

I have center drills, not sure if my live center has a 60' tip, I'll check.

Thanks for saying I'm almost there, the improvement is noticeable but the results are still mildly frustrating.
 
AlfromNH said:
Thanks guys, I hadn't noticed the double cuts. I was trying to hit the half nut at the "1" everytime, I don't think I missed it by more than 1/4 of an increment, but I'll pay closer attention.

I have center drills, not sure if my live center has a 60' tip, I'll check.

Thanks for saying I'm almost there, the improvement is noticeable but the results are still mildly frustrating.
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A quarter of an increment will cause what you are seeing. At least for me, I have to be at maximum attention to single point thread. Have to be on the mark every time for a nice looking thread. That takes practice and minimum distractions.

Getting closer!
 
you might try slowing your RPM down. I thread at 80rpm, slow as the lathe will go. 500 rpm sounds wildly fast and is likely the reason for you missing the index mark on your threading dial.Keep experimenting and asking questions and you will end up with great threads.
 
wildcatter said:
you might try slowing your RPM down. I thread at 80rpm, slow as the lathe will go. 500 rpm sounds wildly fast and is likely the reason for you missing the index mark on your threading dial.Keep experimenting and asking questions and you will end up with great threads.
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Yeah, I usually thread at pretty low speeds myself. It's easier to catch your mistakes that way, if you should make one. Makes it a whole lot easier to thread to a shoulder if the speed is lower!
 
Thanks guys. I meant to report back, I made a couple more attempts yesterday with lousy results. I discovered a fair bit of fore/aft play on the compound, so I’m correcting that before another attempt.
I’m glad to hear slower speeds are acceptable, that sounds like it will make the process a lot easier.
 
Not having a lot of shop time lately, but here’s my latest attempt. Better, but the threads have a saw tooth shape, and the od is still not consistent
00DE9379-5D5A-4157-8B65-6A9619E91903.jpeg
 
Set the compound slide straight, the same way you would do when turning. That way, you have one point of failure less.
Place the tool perpendicular to the stock.
Run at the slowest speed you lathe can run.
Leave the half nuts engaged. Stop the lathe at the end of the thread, backoff the tool, reverse the rotation and reverse the carriage using the motor. That way you can't miss the threading dial and have one point of failure less.
Now thread using some kind of lubrication and check the thread at every pass. Make a picture of every pass. You can stop when the thread is starting to look ugly,
Make a note of the threading depth at every pass.
Make a picture of the setup (from above the tool post) showing the tool (setup).
Do the first pass at 0.1 mm (0.002") cutting depth, the remaining at 0.05 mm (0.001"). It is not a speed contest but a way to get started and find the problem.
 
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